A superconducting accelerating cavity is a device for accelerating charged particles such as electrons, positrons, and protons by means of an accelerating electric field generated inside the cavity by an input of high-frequency power. When the inner surface of the main body of the superconducting accelerating cavity is not smooth, or when impurities are present on the inner surface of the main body, heat generation or electrical discharge is induced, which degrades the performance of accelerating the charged particles.
It is a known practice to perform electropolishing in order to smooth the inner surface of the main body of the superconducting accelerating cavity and remove impurities from the inner surface (e.g., see PTL 1). Eiectropolishing of the superconducting accelerating cavity is performed with an electrode installed on each of the inside of the cavity main body and the outer surface of the cavity main body, while the cavity main body is filled with an electrolyte.